[Proj] Missing proj_def.dat in 4.9.1 release

[Roger Bivand]

Please may I ask when a new release will be forthcoming to remedy the
serious shortcoming of the 4.9.1 release? This has now propogated and is
causing chaos in uses in the R world. For example, the Debian proj-data
package does not have proj_def.dat, I don't know about other distributions.
In reply to my report on Trac 19 May: 

"different behaviour across platforms: pj_init_plus" #274 

https://github.com/OSGeo/proj.4/issues/274

and apparently fixed by hobu 27 May. Trunk has the forgotten file, but we
are now seeing widening repercussions of its absence in the 4.9.1 release,
because users are installing plugins/packages for R built against this
release. We have manually added the missing file to the proj/ folder for our
Windows and OSX binary packages, but cannot protect users installing the
packages/plugins from source.

Should a new release not be forthcoming, how may one recover the absolute
path of a file found by pj_open_lib() to determine the directory in which
the other files reside? Currently this is a PAFile, and recovering its file
descriptor isn't obvious. If I had that, I could copy all the PROJ_LIB files
to a temporary directory, add a copy of missing proj_def.dat, and set
PROJ_LIB to suit for the duration of the R session (or until the package
(plugin) was unloaded).